Had something similar with an HP desktop I bought for my mother. I could not find the video port on it, and it seemed like it wanted an HDMI connection to her monitor. I kept looking though, and finally realized that there was a spot that looked like a port covered with a metal plate. I took the plate off, there was the "classic" monitor port, worked like a champ.

I recall being more amused than anything else.....pretty silly though.